Mode
Most commonly occurring value
Median
Middle values when all values ordered low to high
Mean
Arithmetically derived average value
A histogram (effectively bar chart) shows….
The distribution of a scale variable using banded categories (e.g value ranges)
The tallest point of a histogram can be referred to as…
The modal point
What can the modal point be used for?
To infer the typical or average value in the data
Variation indicates…
The extent to which values deviate from the typical (I.e average) value
The standard deviation is….
Sensitive to skewness
Skewness will inflate…
the size of the standard deviation
Skewness
Tells you whether cases are dispersed similarly either side of the centre (symmetrical) - think of a line graph
Positive skewness (line graph)
Most cases towards the left with a long tail to the right
Negative skewness (line graph)
Most cases towards the right with a long tail to the left
Symmetrical skewness (line graph)
Cases are evenly dispersed either side of the mean
How can skewness be measured as a numerical value?
Using skewness statistic, score of 0 means no skewness, values more extreme than +/-1 indicate the median and interquartile range are better than the mean and standard deviation
Positive Skewness (box plot)
Most cases towards the bottom with a long tail to the top
Negative Skewness (box plot)
Most cases towards the top with a long tail to the bottom
Symmetrical (box plot)
Cases are evenly dispersed either side of the median
Dependant variable
The variable we are trying to measure (through manipulating the independent variable)
Independent variable
The variable we are manipulating to measure the dependant variable
Internal validity
The extent to which we can say the dependant variable was not effected by any variable other than the independent variable
Measurement validity
Do the measures effectively grasp the concepts we are trying to measure
